Decoding apparatus



Patented Dec. 8, 1942 County, Pa., assignor toll-he -Union -Switch& Signal Company, Swissvale, Pa., a ,corporation of Pennsylvania Application February 25, 1941, Serial No.380,`415

l Cl. 246-34) 9 Claims.

My invention relates to decoding apparatus, and -it has particular reference to the provision of apparatus `of the class which enables codes of the time code type to be decoded by a group of relays. More particularly, my invention has reference to the provision of apparatus for use in coded railway signal systems, and which apparatus is eiective to decode time codes by measuring the duration of the cycles oi such codes.

An object of my invention is tc provide novel and improved apparatus for decoding codes which are diierentiated from one another by the relative lengths or durations of the indi- Another object is to provide novel and '1m- .prcved apparatus for Ydecoding vcodes comprising recurrent cycles each consisting of one on and `one off interval during whichv energy does and does not flow respectively, and which codes diier from one another by being cornprised of individual code cycles which have diiferent durations.

An additional object is to provide novel and improved apparatus for differentiating codes in accordance with the relative durations of the individual code cycles comprising such codes, irrespective oi the relative durations of the on and ofi intervals comprising such codes.

A further object is to provide novel and improved deccding apparatus for differentiating codes in accordance with the relative durations of the individual code cycles comprising such codes irrespective oi the relative durations of the on intervals -of the diierent code cycles comprising such codes.

Another object is to provide novel and improved apparatus ior decoding codes by a group of timing relays.

An additional object is to provide novel and improved decoding apparatus having a code responsive device operated from one position to another in response to each on interval or a code, and incorporating means rendered effective by such device in its other position for maintaining the device in such other position for a given interval oi time irrespective of the duration of the on intervals of the code cycles constituting such codes.

The above-mentioned and other important objects and characteristic features of my invention which will become readily apparent from the following description, are attained in accordance.

with my invention by utilizing a code following device operated from one position to another upon receipt of an on interval of lcode energy,

by providing means rendered effective when the device reaches its other position for 'maintaining the device in such position'for a 'gven'in- Aterval irrespective of the duration of the "1on4 interval of energy actuating the device, and by providing decoding relays lwhich measure the time interval intervening between said given interval and the next succeeding on interval of the code. In accordance with the duration of the measured time interval, the decoding relays are 'selectively actuated or controlled "and selective Vcontrols are established according `'to the duration oi the measuredtimeinterval.

uNiy invention also resides in 'the arrangement Vci apparatus into novel decoding systems "and paratus embodying my invention 'incorporated into a signal vsystem provided for a stretch of railway track. Fig. 2 nis `a chart or `diagrammatic time table of `the sequence of operation ci the relays shown in'liig. v1 under 'the'several different conditions f code employed. Fig. 3 isa diagrammatickeyto the symbls employed in .'Fig. .2.

Referring -to "Fig l, the reference character Xv designates a stretch f railway track over lwhich trahie normally moves'in the eastbound direction, or from left to right as viewed in the drawing, and'which stretch is provided with a V.signal system incorporating novel deco/ding apparatus embodying my invention. In accordance withthe usual practice, the rails l and la oi Ythe stretch are divided by insulated joints 2 finto aplurality of successive adjoining track sections, of which only one section, `D-E, is represented complete in the drawing.

#Each f the sections of track X'is provided adjacent its entrance end with a signal, designated by the reference character Si with a suitably distinguishing suflix, for-.governing trai- .cin the normal direction of traiiic movement. The signals Sinay4 be of anysuitable form, such as semaphore, searchlight, position light, etc., but for'the purposes of the'iollowing description Ait will be assumed that the signals are ofthe color. light type "comprising aplurality of lamps.

f SignalSD, 'for example,comprises fourr lamps '6, `'Lt and- 9, These lamps arefadapted to be selectively energized and may be utilized for controlling traffic on stretch X in a manner to be made clear presently.

The rails of section D-E are incorporated into a track circuit which comprises, in additionto the track rails, a track relay TRD connected to the rails at the entrance end D of the section and suitable trackway energy transmitting apparatus located at the exit end E of the section for supplying energy to the track circuit. The trackway energy supplying means for each section comprises a suitable source of current, which may be either a source of unidirectional current or a source of alternating current; a code or impulse generating means for generating codescomprising recurrent cycles each consisting of an on interval and an off interval during which energy does and does not ow respectively; and suitable means for selecting the particular one of such codes for transmission through the track circuit in accordance with trafc conditions in advance.

These trackway energy supplying means are arranged to provide the associated track circuit with one or another of a plurality of codes each comprising recurrent code cycles which are differentiated from one another by the relative durations or lengths of such cycles. Each code cycle comprises an on interval followed by an off interval, and, as will be readily apparent hereinafter, the decoding apparatus embodying my invention is adapted to decode such codes in accordance with the relative durations of the code cycles comprising such codes irrespective of the relative durations of the on and off intervals comprising such cycles. coding apparatus embodying my invention functions to decode codes comprising cycles varying in duration but not shorter in duration than a given interval, hereinafter mentioned, and the on and off intervals of such cycles may have any relative proportion provided that the on intervals of such cycles do not exceed the given interval. Thus, for example, the codes may comprise cycles each having on intervals equal in duration, followed by off intervals which have different durations for different codes so as to provide code cycles having different durations. The on intervals of code in such case may be of relatively short duration separated from each other by o periods or intervals varying in duration, r similar, for example, to the impulse type codes shown and described in United States Letters Patent No. 2,197,414, granted on April 16, 1940, to Willard P. Place, for Signal systems; or such on intervals may be of relatively long duration separated from each other by relatively short off periods varying in duration. On the other hand, the on intervals of the diierent codes may be of different durations separated from each other by off intervals of equal duration; or the cycles may be comprised of on and off intervals having durations equal for a given code but differing for different codes. It follows, therefore, that the different codes may be comprised of on and off intervals having any relative proportion provided that the durations of the code cycles differ for different codes but do not have a duration shorter than the given interval previously mentioned, and that the durations of the on intervals of such codes do not exceed such given interval.

A typical arrangement of apparatus for supplying trackway energy to the track sections of stretch X is represented in the drawing adjacent That is to say, the dethe exit end D of the section next in the rear or 75 extending to the left as viewed in the drawing, from section D-E. In the particular arrangement illustrated, a direct current source such as a battery not shown but having its terminals designated by the reference characters B and C, is represented as supplying on impulses of relatively short duration to the track rails through the medium of impulse generating means. These means comprise a track transformer, designated by the reference character TT with a distinguishing suffix, which has its secondary winding I0 connected to the track rails at the exit end of the associated section, and which transformer has its primary winding II connected in multiple with a condenser I3 and supplied with unidirectional current from the source periodically interrupted or coded through the medium of suitable interrupting or code transmitting apparatus. The code transmitting apparatus may be of any desired type, and as shown comprises a plurality of code transmitters or coders, designated by the reference character CT with a suitably distinguishing suf x, each operating a contact member I2 at a different rate. For the purposes of the present description, I shall assume that coders CT'I5, CT52 and CTIJ operate their associated contact members I2 at the rate of 75, 52 and 40 times per minute, respectively. It follows that a contact member I2 of a coder, when interposed in a circuit supplied with energy, periodically interrupts or codes such energy at the rate of 7 5, 52 or 40 times per minute, and that such coding comprises recurrent cycles each consisting of an on interval of current ow when the contact member of the code transmitter is in its upper or closed position, followed by an off interval during which no current flows when the contact member of the coder is in its released or opened position. It is also apparent that the 75, 52 and 40 codes are differentiated from one another by the relative lengths or durations of the individual code cycles comprising such codes.

For the purpose of more clearly dening my invention, I shall refer hereinafter to cycle units, and I shall assume that 60 cycle units equal one second. The code cycles of the 75 code, for example, have a duration of of a second and thus may be expressed as having a duration of 48 cycle units; the code cycles of the 52 code have a duration of 69 cycle units; while the code cycles of the 40 code have a duration of 90 cycle units.

Each contact member I2 of the coders CT is interposed in one or another of a plurality of circuits, shortly to be traced, each of which includes the primary winding Ii of transformer TTD and condenser I3 connected in multiple therewith. It follows that each time the direct current source is connected to transformer TTD through a contact member I2 0f a coder CT, energy is stored in the circuit of the transformer and condenser, and each time such contact opens, the stored energy rapidly collapses and causes to flow in the track circuit a relatively short impulse of energy. These on impulses of energy in the track rails are of substantially the same relative duration irrespective of the rate of operation of the coder contact member I2 over which energy is supplied to the transformer and condenser, but the durations of the ofi intervals when no energy is applied to the track rails will of course vary in accordance with the particular contact member I2 employed, hence these contacts function to differentiate the codes by varying the durations of the code cycles which may be considered as comprising the interval between successive openings of a coder contactv member I2.

The impulses of energy applied to section D E by the trackway energy transmitting apparatus at the exit end E of the section, which apparatus is not shown in the drawing but which substantially corresponds to the apparatus represented provided at D and heretofore described, are received by code following track relay TRD when the section is unoccupied. Relay TRD picks 'up in response to each on interval of energy in the track rails, to actuate decoding apparatus effective to dilierentiate between the cedes in the track by measuringthe relative durations of the cycles constituting such codes.

The decoding apparatus comprises a code responsive device or relay M; a plurality of interval measuring devices one for measuring a rst yinterval i time equal in duration to the heretoiore mentioned given interval and the others for measuring other intervals of time; and a group of code registering relays Yfor detecting and registering the relative durations of the cycles of codes in the track.

The interval measuring devices, as shown, comprise slow acting relays IR, 2R, AR and BR. Relays IR and 2R are energized over an easily traced circuit which extends from terminal B through back contact I5 of relay M, back contact I6 of relay IR, and the windings of relays IR and 2R in multiple to terminal C. Relay 2R when picked up closes its front contact I'I to close a stick circuitvpath connected in multiple with back contact IB of relay IR, so that relays 2R and IR are maintained energized over this stick circuit path after relay IR picks up. Relay IR is proportioned to be slightly slowervin picking up than relay 2R, thereby enabling the latter relay to close its front contact II and complete the previously -mentioned stick circuit path -prior to relay IR opening its back Contact I6.. Both relays IR and 2R are represented as having asymmetrical units I8 connected, in opposition to the flow of current energizing such relays, across their respective terminals to assist in providing such relays with slow release characteristics. Relay IR is proportioned to Yhave a slow release period shorter in duration than relay 2R,

and to correspond with the heretofore assumed 75, 52 and 40 code rates, which comprise code cycles having durations oi 48, 69 and 90 cycle units, respectively, relay IR preferably has a slow release period of cycle units. Relay 2R is proportioned to have a slow release interval longer in duration than the duration of the on interval of any of the codes, but shorter than the duration of any of the cycles comprising such codes. The given interval measured by the slow release period of relay 2R may, for example, have a duration of 36 cycle units. This interval is, of course, shorter in duration than the sh0rtest cycle of code employed i. e. 48 cycle units.

Relay AR is energized over a pick-up circuit extending from terminal B through front contact I5 of relay M, front contact I9 of relay 2R, back contact 2D of relay IR and the winding of relay AR to terminal C, and this relay is provided with a stick circuit path in which its front contact ZI shunts back contact 20 of relay IR in the just traced pickup circuit for relay AR. Relay BR is provided with a pick-up circuit including iront contact 22 of relay AR and the upper winding of relay BR, and this relay is provided with a stick circuit which passes from terminal B through frontcontact I5 of relay M, front contact I9 of y-relay 2R, front contact 23 of relay BR and the lower winding of relay BR to terminal C. Each relay AR and BR is provided with an asymmetrical lunit I8 connected across its terminals to vaid in providing such relay with slow release characteristics. Relay AR is proportioned tohave a slow release period at least as long in duration as the difference (l2 cycle units) between the release period of relay 2R (36 cycle units) and the length (48 cycle units) of the shortest code cycle employed, but shorter in duration than the difference (33 cycle units) between the release period of relay 2R and the length (69 cycle units) of the second shortest code cycle employed. For convenience, relay AR will be assumed in the following de# scription to have a release interval of, say, 22 cycle units. Relay BR is proportioned to have a release period sufficient so that the release periods of relays AR and BR, taken successively, have a duration longer than the difference (33 cycle units) between the release period of relay 2R and the second shortest code cycle employed, but which duration is shorter than the difference (54 cycle units) between the duration of lthe release period of relay 2R and the length (90 cycle units) of the longest code cycle employed. The release period of relayl BR thus will vary in accordance with the release interval selected for relay AR, and for the purposes of this description it will be assumed that relay BR has a releaseperiod of 22 cycle units.

The code registering relays are designated by the reference characters FA, ME and SL, re'- spectively. Relay FA is-provided with an energizing circuit extending from terminal B throughtfront contact I5 of relay M, front contact I9 of relay 2R, front contact 29 of relay iR, front Contact 24 of relay AR and the winding of relay FA to terminal C; and the relay preferably is provided with slow releasing characteristics sufficient, at least, to hold the relay in its pickedup position for an interval equal to thedifference A(28 cycle units) between the releaseperiod (20 cycle units) of vrelay IR and the length (48 cycle units) of the shortest code cycle employed. Relay ME is provided with an energizing circuit passing from terminal B through front contact I5 of relay M, front contact I9 oi relay 2R, front contact 2U of relay IR, back contact 24 of relay AR, front contact 25 of relay BR, and the winding of relay ME to terminal C; and this relay preferably has a slow release interval equal in duration to the diiierence (49 cycle units) between the release period of relay IR and the length (69 cycle units) of the second shortest code cycle employed. Relay SL is energized over a circuit which substantially corresponds to the circuit of relay ME except that back contact 25 of relay BR and the winding of relay SL replace respectively front contact 25 of relay BR and the winding of relay ME. Ret lay SL preferably is provided with a slow release period which enables the relay to bridge the dif ference (70 cycle units) between the release period of relay IR and the length (90 cycle units) `of the longestcode cycle employed.

The code registering relays FA, ME and SL cooperate in controlling signal SD in the following manner: When all of the code registering relays are released, as shown, lamp 9 of signal SD isenergized overa circuit extending from terminal B through back contact 26 oi relay FA,

Nback contact 2l of relay ME, back 'Contact 28 t relay SL and the filament of lamp 9 to terminal C. The illumination of lamp 9 may be employed as the most restrictive indication of the signal, indicating for example that the associated section is occupied. When relay SL is picked up and relays FA and lWE are released, lamp 8 of signal SD is illuminated-over a circuit extending from terminal B through back contact 26 of relay FA, back contact 21 of relay ME, front contact 28 ofV relay SL and the filament of lamp 8 to terminal C. The illumination of lamp 8 may be employed as an indication less restrictive than that of lamp 9 but more restrictive than that of any other lamp. When relay m is picked up but relay FA is released, lamp 'I is illuminated over an obvious circuit including back contact 26 of relay FA and front contact 21 of relay ME, and the illumination of such lamp may be employed as an indication less restrictive than those of lamps 8 and 9 but more restrictive than that of any other lamp. When relay FA is picked up, lamp 6 is energized over an obvious circuit including front Contact 26 of relay FA, and the illumination of this lamp may be utilized as the least restrictive indication of the e signal.

The code registering relays further cooperate in controlling the supply of trackway energy to the section next in the rear of section D-E.

When all code registering relays are released, as

shown in the drawing, the section in the rear of section D-E is supplied with 40 code energy over a circuit which extends from terminal B through back contact 29 of relay FA, back contact 30 of relay ME, back contact 3| of relay SL, contact I2 of coder CTM), primary winding II of transformer TTD and condenser I3 in parallel, to terminal C. When however relay SL is energized and relays FA and ME are devenergized, the section in the rear of section D-E is supplied with 52 code energy over a circuit which extends from terminal B through back contact 29 of relay FA, back contact 30 of relay ME, front contact 3| of relay SL, contact I2 of coder CT52 and primary winding II of transformer TTD in multiple with condenser I3, to terminal C. Whenever relay FA is picked up to close its front contact 29, or relay FA is released to close its back contact 29 and relay ME is picked up to close its front contact 30, the section in the rear of section D-E is supplied with 75 code energy over a circuit which includes Contact I2 of coder CT'IE.

The above-mentioned controls of signal SD and of the energy supplied to the section in the rear of section D-E are effected in the following manner by the decoding apparatus differentiating the diierent code rates of energy applied to the section.

When section D-E' is occupied by a train, such as train W represented in the drawing, the coded energy applied at El to the section is shunted by the train away from relay TRD, and as a result relay TRD is inactive and its front contact 33 is held steadily open. Relays M, AR,

BR, FA, ME and SL are released, but relays IR and 2R are energized since back contact I5 of relay M is steadily closed. Lamp 9 of signal S-D is energized, and the previously traced circuit over which 40 code is supplied to the rear section is completed. The section next in the rear of an occupied section is, therefore, supplied with 40 code energy.

When the train vacates section D-E and occupies the section next in advance, section D-E is supplied with 40 code energy. Relay 'TRD of course responds to such coded energy and closes its front contact 33 each time an on impulse of energy is in the track rails. When relay TRD closes its front contact 33 in response to the first on impulse of 40 code energy received in the rails of section D-E, relay M is picked up and closes its front contact 34 to complete an obvious stick circuit which includes front contact 35 of relay 2R. Relay M also opens its back contact I5 to deenergize relays IR and 2R, but such relays remain up for their respective slow release intervals. Relay SL is now energized over its previously traced circuit, and picks up to shift the coding of current supplied to the rear section from the 40 to the 52 code rate; and also to shift the energization of the lamps of signal SD from lamp 9 to lamp 8.

Relay IR drops at the end of its slow release interval or 20 cycle units after relay M picks up, and front contact 20 of relay IR opens to deenergize relay SL while back contact 20 of relay IR closes to energize relay AR. Relay AR accordingly picks up to close its front contact 22, whereupon relay BR also picks up, and front contacts 2| and 23 of relays AR and BR are closed to complete respectively the stick circuits of such relays. Relay 2R next releases at the end of its slow release interval (36 cycle units after relay M picks up or 16 cycle units after relay IR releases), and opens its front contact I9 interposed in the stick circuit 0f relays AR and BR. In addition, relay 2R opens its front contact 35 interposed in the stick circuit of relay M, and since it has been assumed that the release interval of relay 2R exceeds the duration of the on interval of any of the codes, relay TRD is at this time released so that relay M is deenergized and releases. With relays M and IR released, relay 2R first picks up, and then relay IR picks up, and these two relays are held up over back contact I5 of relay M until relay TRD responds to the next succeeding on interval of energy received from the section. Relays AR and BR, however, release prior to relay TRD responding to the next succeeding on impulse of the 40 code, so that when relay TRD picks up in response to such on impulse to reenergize relay M, relay SL is again energized. The slow release interval of relay SL, as mentioned heretofore, is selected to hold such relay up for an interval ('70 cycle units) substantially equal to the difference in duration between the length of the longest code cycle and the release period of relay IR. With relays M and SL energized and relays IR and 2R deenergized, the apparatus repeats the cycle of operation previously described, and this operation is, of course, repeated each time an on interval of 40 code energy is received by relay TRD from the track rails.

When section DE and the section next in ad- Vance are unoccupied, and the second section in advance of section D-E is occupied, 52 code energy is supplied to section D-E. The cycles comprising this code each have a duration of 69 cycle units, hence when the coded energy supplied lto section D-E is shifted from the 40 to the 52 code, the first on interval of such energy actu- 'ates relay TRD to pick up relay M, prior to relay to the '75 code rate, and the energization of the lamps of signal SD is shifted from lamp 8 to lamp Relay BR is energized over its stick circuit when relay M picks up prior to contact 23 of relay vBR opening, and the latter relay is held energized over this circuit until after relay IR drops to pick up relay AR and thus complete the pick-up circuit of relay BR. Relay AR becomes deenergized when relays M and 2R drop at the end of the slow release interval of relay 2R, and, as pointed out heretofore, the slow release interval of relay AR is Selected so that relay AR releases prior to relay M being picked up in response to relay 'IRD responding to the next successive on interval of the 52 code. ergized only after relay AR releases, and the slow release period of relay BR is eiective to hold that relay picked up so that its front contacts 23 and 25 are closed, until relay TRD responds to the next succeeding on impulse of coded energy,y

and relay M accordingly picks up to complete the previously mentioned stick circuit of relay BR and the previously mentioned energizing circuit of relay ME. The slow release period of relay ME is selected so as to enable that relay to bridge the interval (49 cycle units) intervening between the releasing of relay IR and the picking up of relay M in response to relay TRD being actuated by the next succeeding on interval of the 52 code. The above described operation of the apparatus is, of course, cyclically repeated as long as 52 code energy is received by relay TRD from the track rails.

When section D-E and at least the two sections immediately in advance vof that section are unoccupied, section D-E is supplied with 75 code energy which as pointed out heretofore, is comprised of code cycles each having a duration of 48 cycle units. It is readily apparent therefore that when the coded energy in section D--E is shifted from the 52 to the 75 code rate, relay TRD is actuated by the rst on impulse of the '75 code prior to relay AR releasing, so that when relay M picks up it completes the previously traced circuit of relay FA through front contacts of relays M, IR, 2R, AR and BR. Relays IR and 2R are deenergized when relay M picks up, relay FA is deenergized when relay IR drops at the end of its slow release period, relay AR is energized until relay 2R drops at the end of its slow release period, while relay BR remains energized since relay M is caused to pick up due to relay TRD following 75 code energy, prior to relay AR dropping, and when relay M picks up relays FA, AR and BR are reenergized- Relays FA and AR are provided with slow release characteristics selected to maintain such relays in their respective picked-up positions during the lintervals that they are deenergized when relay TRD follows 75 code. It follows, therefore, that relays FA, AR and BR are maintained in their respective picked-up positions in response to '75 code energy and that the decoding apparatus embodying my invention cyclically repeats the operation just described as long as '75 code energy is received by relay TRD from the rails of the section.

It is, of course, readily apparent that when relay FA is selected for energization, lamp 6 of signal SD is energized while lamp 'I is deener- Relay BR of course becomes deen- 'j table is shown in Fig. y3. From an inspection of these two figures, it can readily be ascertained when the coil circuit of any relay is closed, when the relay picks up its front contacts, when its coil circuit is opened and when its front contacts are released. Y

Although I have herein shown and described only one form of decoding apparatus embodying my invention, it is understood that various changes and modications may be made therein within the scope of the appended claims with- -out departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

l. In combination with a control circuit supplied with one or another of a plurality of codes each comprising recurrent code cycles consisting oi an on interval followed by an off interval during which energy does and does not flow respectively, said on intervals of the different codes each being not longer in duration than a given interval of time and said codes diiering from each other in the relative durations of the code cycles, means operable by energy received from said circuit for picking up a relay in response to each on interval of energy in said circuit, other means operable upon receipt of an on interval of energy for maintaining such relay energized for said given interval regardless of the duration of the received on interval of energy, and decoding means controlled by'said relay and selectively responsive to the relative durations of the code cycles of such codes.

2. In combination with a rstretch of railway track supplied with one or another of a plurality of codes each comprising recurrent code cycles consisting of an on interval followed by an off interval during which energy does and does not ilow respectively, said on intervals of the different codes each being not longer in duration than a given interval of time and said codes differing from each other inthe relative durations of the code cycles, means operable by energy received from the rails of said stretch for picking up a vrelay in response to each on interval of energy in the rails, other means voperable upon receipt of an on interval of energy for maintaining said relay energized for said given interval regardless of the duration of the received on interval of energy, and decoding means controlled jointly by said relay and by said other means and selectively responsive to the relative durations of the code cycles of said code.

3. In combination with a stretch of railway track supplied with one or another of a plurality of codes each comprising an on interval of current flow not longer ,in duration than a given interval and an off interval having one or another of a plurality of durations, a code following relay receiving energy from the rails, means operated by said relay in response to a receipt of an on interval of current, other means 'effective upon operation of said first means for maintaining said rst means operated for said given interval regardless of the length of said on interval of current, and decoding means controlled jointly by said first means and said second means and selectively responsive to the durations of the 01T intervals between successive on intervals of the different codes,

4. In combination with a stretch of railway track supplied with one or another of a plurality of codes each comprised of cycles consisting of an on interval of energy not longer in duration than a given interval and an off interval having one or another of a plurality of durations, a relay operated in response to each energy impulse in the rails, means operable upon operation of said relay for maintaining said relay operated for said given interval regardless of the length of said on interval, and decoding means controlled jointly by said relay and by said firstmentioned means and selectively responsive to the relative durations of the oif intervals of the cycles constituting said codes.

5. In combination with a stretch of railway track supplied with one or another of a plurality of codes each comprising recurrent code cycles consisting of an on interval followed by an off interval during which venergy does and does not flow respectively, said on intervals of the different codes each being not longer in duration than a given interval of time and said codes differing from each other in the relative durations of the comprised code cycles, a first relay, means operable by energy received from the rails of said stretch for picking up said relay in response to each on interval of energy in the rails, a second relay energized over a back contact of said rst relay and having a slow release period equal in duration to said given interval, means controlled by said second relay for maintaining said first relay energized for said given interval regardless of the relative durations of the received on intervals of energy, and decoding means controlled jointly by said first relay and by said second relay and selectively responsive to the relative durations of the code cycles of said codes.

6. In combination with a control circuit supplied with one or another of a plurality of codes each comprising recurrent code cycles consisting of an on interval followed by an off interval during which energy does and does not flow respectively, said on intervals of the different codes being not longer in duration than a given interval of time and said codes differing from each other in the relative durations of the comprised code cycles, a first relay, means operable by energy received from said control circuit for picking up said relay in response to each on interval of energy in said circuit, a second relay energized over a back contact of said rst relay and having a slow release interval equal in duration to said given interval, means rendered effective when said first relay picks up and controlled by said second relay for maintaining said first relay energized for said given interval regardless of the relative durations of the received' v on intervals of current from said circuit, a

third relay energized over a back contact of said first relay and having a slow release period shorter in duration than said second relay, and decoding means controlled jointly by said first and second and third relays and selectively responsive to the relative durations of the code cycles of said codes.

7. In combination with a stretch of railway track supplied with one or another of a plurality of codes each comprising recurrent code cycles consisting of an on interval followed by an olf interval during which energy does and does not iiovv respectively, said on intervals of the different codes each being not longer in duration than a given interval of time and said codes diifering from each other in the relative durations of the comprised code cycles, a first relay, means operable by energy received from the rails of said stretch for picking up said relay in response to each on interval of energy in the rails, a secondrelay and a third relay, said second relay having a slow release interval equal in duration to said given interval and said third relay having a release interval shorter in duration than said given interval, an energizing circuit for said second relay including a back contact of said first relay and a back contact of said third relay in series, another energizing circuit for said second relay including a back contact of said first relay, a front contact of said second relay and the windings of said second and third relays in multiple, means rendered effective when said first relay picks up and controlled by said second relay for maintaining said first relay energized for said given interval regardless of the relative durations of the on intervals of energy received from said rails, and decoding means controlled by said first and second and third relays and selectively responsive to the relative durations of the code cycles comprising said codes.

8. In combination with a control circuit supplied with one or another of a plurality of codes each comprising recurrent code cycles consisting of an on interval followed by an off interval during which energy does and does not flow respectively, said on intervals of the dilferent codes each being not longer in durationthan a given interval of time and said codes differing from each other in the relative durations of the comprised code cycles, a first relay, means operable by energy received from said circuit for picking up said relay in response to each on interval of energy in said circuit, a second relay and a third relay each energized over a back contact of said first relay, said second relay having a slow release period equal in duration to said given interval of time and said third relay having a slow release period shorter than said second relay, means eifective when said first relay picks up and controlled by said second relay for maintaining said iirst relay energized for said given interval regardless of the relative durations of the received on intervals of current, a fourth relay having a pick-up circuit including a front contact of said first relay, a front contact of said second relay and a back contact of said third relay and provided with a stick circuit including a front contact of said second relay, said fourth slow lrelease relay having a slow release interval shorter in duration than the difference in duration between the longest and the shortest code cycle supplied to said circuit, a fth relay having a pick-up circuit including a front contact of said fourth relay and a stick circuit including a front contact of said second relay and also having a slow release interval, and a plurality of decoding relays controlled by said first, second, third, fourth and fth relays and selectively energized in accordance with `the relative durations of the code cycles comprising said codes.

9. In combination with a stretch of railway track divided into a plurality of successive adjoining track sections, a signal for each section, means for supplying the rails of each of said sections with energy coded at one or another of a plurality of codes each comprising recurrent code cycles consisting of an on interval followed by an off interval during which energy does and does not flow respectively, said on intervals of the different codes each being not longer in duration than a given interval of time and said codes differing from each other in the relative durations of the comprised code cycles, a rst relay for each section, means operable by energy received from the rails of the associated section for picking up the said first relay of that section in response to each on interval of energy in the associated section, other means for each Section operable upon receipt of an on interval of current from the rails of the associated section for maintaining said first relay energized for said given interval regardless of the relative durations of the received on intervals of current, decoding means for each section controlled by the associated relay and by said other means and selectively responsive to the relative durations of the code cycles of said codes, and means controlled by said decoding means for controlling the associated signal and for controlling the supply of current to the section next in the rear of said associated section.

NORMAN F. AGNEW. 

